1. Field of the Invention
This invention concerns a nozzle adjustment mechanism for a radial-flow variable-capacity turbine which may be used as a supercharger (an exhaust turbocharger) for an internal combustion engine. This type of radial-flow variable-capacity turbine is so constructed that the operating gases pass through a number of variably angled nozzle vanes from a coil-shaped scroll in the turbine casing, and the gases are made to flow to the turbine rotor so that they drive the rotation of the rotor.
2. Description of the Related Art
In recent years, if an internal combustion engine has a supercharger, it has become more and more common for it to be the kind of supercharger with a variable-capacity turbine. Such a turbine varies the flow rate of the exhaust gases transported from a coil-shaped scroll to the turbine rotor according to the operating state of the engine, and it does this variation in such a way as to match the flow rate of the engine exhaust gases to that rate which would produce the optimal operating condition of the supercharger.
The basic structure of a conventional supercharger is shown in FIG. 7 and FIG. 8. FIG. 7 is a perspective drawing of a supercharger with a variable-capacity turbine belonging to the prior art, and FIG. 8 shows an example of how link plate 3, nozzle vanes 2, and lever 1 are connected in the previous art. In FIG. 7, 10 is the turbine casing and 11 is the coil-shaped scroll in the outer periphery of the turbine casing 10. Number 12 is the turbine rotor, which is supported on the center of the casing by bearings (not pictured) such that it is free to rotate. The rotor is coaxial with the compressor (also not pictured).
Number 2 is a nozzle vane, a number of which are arranged in spaces along the circumference of the turbine on the inner periphery of the scroll 11. Nozzle shafts 02, on the inner extremity of the nozzle vanes 2, are supported in nozzle mounts 4, which are fixed to the turbine casing 10, such that they are free to rotate so that the angle of the nozzle vanes varies. 14 is the gas exhaust casing which guides the exhaust gases out of the engine once the gases have completed the work of expanding to drive the turbine rotor 12. The gas exhaust casing is fixed to the turbine casing 10.
Number 3 is a disk-shaped link plate. It is supported by the turbine casing 10 in such a way that it is free to rotate. Indentations 3a are provided along the periphery in which levers 1, which will be discussed shortly, can engage. Number 07 is an actuator which drives nozzle vanes 2 through the link plate 3. Number 005 is a lever which connects an actuator rod 7 of the actuator 07 to the link plate 3.
FIG. 8 shows how the link plate 3, levers 1, and nozzle vanes 2 are assembled. The indentations (oblong holes) 3a are provided on the inner periphery of the disk-shaped link plate 3, at regular intervals along the circumference of the turbine. Bosses 6, formed on the outer extremities of levers 1, engage in the indentations (oblong holes) 3a in such a way that they can rotate and scrape the surface of the indentation. The nozzle shaft 02 of each nozzle vane 2 is fixed to the inner extremity of one of the levers 1.
In this sort of variable-capacity turbine, the reciprocating displacement of the actuator 07 is transmitted to the link plate 3 by way of actuator rod 7 and lever 005 of the crank mechanism, thus driving the rotation of the link plate 3. When the link plate 3 rotates, the bosses 6 of the levers 1, which are engaged in indentations 3a of the link plate 3, move along the circumference of the link plate. Nozzle shafts 02, which are fixed to the interior extremities of the levers 1, thus rotate. This causes nozzle vanes 2 to rotate, changing the angle of their vanes.
In the variable-capacity turbine pictured in FIGS. 7 and 8, bosses 6 on the outer extremities of levers 1 engage in indentations 3a, which are provided on the inside of disk-shaped link plate 3 at regular intervals along the circumference of the turbine. The nozzle shafts 02 of nozzle vanes 2 are fixed to the interior extremities of the levers 1. Most variable-capacity turbines described above are used as exhaust gas turbines in the superchargers of automotive internal combustion engines. Such superchargers are small, so nozzle shaft 02 and the connecting hole of the nozzle vane 2 must have a small diameter, and with respect to strength, they will never be able to sustain much force. In general, therefore, the connection between nozzle vane 2 and lever 1 is made by pressing in order to secure the strength. In the prior art design shown in FIGS. 7 and 8, the edge of nozzle shaft 02 is pushed into the connecting hole in lever plate 1, and the connecting hole grips the edge of nozzle shaft 02. The end of the nozzle shaft is then riveted or welded so that nozzle vane 2 and lever 1 cannot rotate with respect to each other, but will remain fixed. Thus nozzle vane 2 and lever 1 are joined to each other.
In other words, in the technique employed in the prior art, when the connecting hole is made to grip the edge of nozzle shaft 02, both the connecting hole and the edge are forced to undergo deformation. Thus in order to fasten together nozzle shaft 02 of nozzle vane 2 and lever 1, a great deal of force is needed to push the shaft into the connecting hole. When this prior-art technique is used, then, as has been discussed, a small-diameter shaft 02 is forced into a small-diameter connecting hole with great force to join the two together. As a result, there is a chance that the nozzle shaft 02 might break or that some of connecting holes might break off when a large rotary force is applied to the area where the edge of the nozzle shaft 02 and connecting hole are connected, or that the portion where these two members are connected could be damaged.
Furthermore, since nozzle vane 2, being exposed to the exhaust gases, attains quite a high temperature, the portion where the edge of the nozzle shaft 02 goes into connecting hole, where the nozzle vane 2 and lever 1 are joined, also attains a high temperature. As was explained earlier, the connection is achieved by deformation, so its strength at high temperatures will be diminished. This will make the nozzle shaft 02 of nozzle vane 2 more prone to the type of damage mentioned above.
The vane angle of the variable-capacity turbine must necessarily be controlled closely. In the prior art described above, the relative angle of the nozzle vane 2 with respect to lever 1 is set during assembly with the help of a jig. This required a large number of assembly processes as well as special assembly tools such as the jig, driving up the production cost.
In view of these problems in the prior art, the objective of this invention is to provide a nozzle adjustment mechanism for a variable-capacity turbine which would have the following features. The connecting lever to connect the nozzle drive component driven by the actuator to the nozzle vane, and the edge of the nozzle shaft on the nozzle vane, would have a high degree of strength and would not experience deformation. There would be no need for special assembly tools such as a jig, and a highly accurate connection would be achieved with fewer assembly processes and at a lower cost.
The first preferred embodiment of this invention comprises a variable-capacity turbine which has a coil-shaped scroll in the turbine casing. A number of nozzle vanes are arranged along the circumference of the turbine at the inner peripheral side of the scroll and are supported on the turbine casing in such a way that they can rotate to vary the angle of the vanes. A turbine rotor rotates freely on the inner periphery of the nozzle vanes. Operating gases are made to flow from the scroll through the nozzle vanes to the turbine rotor, driving the rotation of the rotor. The turbine has a nozzle adjustment mechanism having a nozzle drive member for the nozzles which is connected to an actuator that causes the nozzle drive member to rotate around the turbine shaft, and a plurality of connecting levers to link the nozzle drive member to the nozzle vanes.
This variable-capacity turbine is distinguished by the following. The connecting hole of the connecting lever has a stopper surface which is flat or curved. The connecting edge of the nozzle shaft also has a stopper surface which corresponds to the stopper surface of the connecting hole. When the connecting edge of the nozzle shaft goes into the connecting hole of the connecting lever, the stopper surface of the connecting edge is brought into contact with the stopper surface of the connecting hole, contacting these non-circular surfaces with each other. This contact can be made without causing any deformation of either surface. After the contact is made, then the fixing process will be applied to the connecting edge. The connector lever and the connecting edge of the nozzle shaft are thus effectively locked together in such a way that neither can rotate with respect to the other. The end of the nozzle shaft, in other words, prevents the shaft""s relative rotation.
As an actual configuration of the connection between the nozzle vane and connecting lever, the stopper surfaces of the connecting hole and the connecting edge can be shaped into two flat surfaces or preferably two parallel flat surfaces which oppose each other. The two flat surfaces on either side of the connecting hole and the connecting edge thus make contact with each other.
Alternatively, according to a second preferred embodiment of this invention, the non-circular shaped connection can be formed by cutting away a portion of a circular connection edge to form a single flat surface and providing a corresponding single flat surface in the circular connecting hole so that these two surfaces can come in contact with each other.
Further alternatively, according to a third preferred embodiment of this invention, the connection can be formed by serrating the connecting edge of the nozzle shaft and providing corresponding negative serrations on the surface of the connecting hole which can engage with the serrations on the nozzle shaft.
With these embodiments, when the connecting edge of nozzle vane engages in the connecting hole of lever, the stopper surfaces of the connecting hole and the stopper surfaces of the connecting edge are brought into contact with each other. The nozzle vane and the lever can thus be joined at a geometrically determined angle without experiencing any deformation. The connecting hole and the connecting edge can be engaged with a minimum of force in such a way that neither can rotate with respect to the other. The rotary force of the nozzle vane can be absorbed by contiguous stopper surfaces of the hole and the nozzle shaft.
With this design, the rotary force of the nozzle vane will not cause the connection area where the connecting hole and connecting edge are joined to fatigue. The nozzle shaft will not break, and the drive force from the link plate can be transmitted readily through the lever to the nozzle vane. Even if the connection area where the connecting hole and connecting edge are joined attains a high temperature, it will not experience deformation. Because the coupling is geometric, the rotational force will not damage the connection area where the nozzle shaft engages in the connecting hole. This design produces a coupling of the lever and nozzle vane which is extremely durable.
In this sort of variable-capacity turbine, the vane angle of nozzle vanes must be controlled very accurately. In these embodiments, when stopper surfaces on the connecting edge of the nozzle shaft come in contact with the connecting surfaces on the connecting hole of the lever, the nozzle vane and the lever are geometrically coupled in a previously determined relationship. It is thus no longer necessary, as in the prior art, to establish the relative angle of the two members with a jig when the nozzle vane and the lever are being assembled. Fewer assembly processes are required, and no special tools such as the jig are needed. This reduces the equipment cost.
In the second embodiment of the coupling of the nozzle vane and the lever plate, the stopper surfaces of connecting hole in the lever and the connecting edge of nozzle vane, which engages in the hole, are created by shaving off one side of the connecting edge to form flat the stopper surface and giving the connecting hole a flat surface with which the connecting edge will come in contact. In this second embodiment, only a single stopper surface on the shaft and lever prevents the relative rotation of the nozzle vane and the lever. Thus the degree of rotational force which can be absorbed by each stopper surface is less than if two surfaces are provided; however, fewer production processes are required.
In the third embodiment of the coupling of the nozzle vane and lever, the inner surface of the connecting hole comprises serrations, and the connecting edge of nozzle vane which engages in this connecting hole also has serrations along its inner surface. When serrations of the connecting hole engage with serrations of the connecting edge, they prevent relative rotation of the nozzle vane and lever. With this third embodiment, the ordinary sort of serrations can be machined, making the parts simple to produce. By changing the orientation at which the two serrated surfaces engage, the relative positions of nozzle vane and link plate are easily adjusted.